[ifmgmt] Make "ifstat" show the link-layer protocol for each netdev

[ifmgmt] Make "ifstat" show the link-layer protocol for each netdev

This is useful on devices that perform auto-detection for ports.
Example output:

    iPXE> ifstat
    net0: 00:11:22:33:44:55 using mt4099 on 0000:00:03.0 (Ethernet) [open]
      [Link:down, TX:0 TXE:0 RX:0 RXE:0]
      [Link status: Unknown (http://ipxe.org/1a086101)]
    net1: 00:11:22:33:44:56 using mt4099 on 0000:00:03.0 (IPoIB) [open]
      [Link:down, TX:0 TXE:0 RX:0 RXE:0]
      [Link status: Initialising (http://ipxe.org/1a136101)]

Signed-off-by: Christian Iversen <ci@iversenit.dk>